Abstract:I agree with Heyes that behavioural tests that can distinguish mentalistic
from non-mentalistic alternatives should be sought. However I suggest that
the theoretical issue is less about the passing of behavioural tests than it is
about the internal mechanisms which enable the passing of the tests, and that it
may be helpful to try and assess the internal mechanisms directly by measuring
brain activities.

The theory of “having a theory of mind” is incredibly loose, and needs to be
tied down even with human subjects. However, there is overwhelmingly greater
evidence for the development of mental state concepts in human infancy, and a
certainty that such concepts function in human adults. There is also some
support for the notion that there is a theory of mind ‘module’ in the human
case, or at least a network of links between the various separately measurable
social skills (Karmiloff-Smith et al. 1995; Fletcher et al. 1995). As a
particular case, contrary to the suggestion and the end of 2.1, there is data
from large samples of children which has been taken to support a very close
correlation between mirror self-recognition and sensitivity to imitation
(Asendorpf and Baudonniere, 1993; Asendorpf, Warkentin and Baudonniere, 1996)
and a large literature relating imitation and other theory of mind tests (e.g.
Azmitia and Hesser, 1993; Vonhofsten and Siddiquit, 1993; Loveland et al. 1994;
Smith and Bryson 1994).

This literature contrasts starkly with the very limited corpus of positive
behavioural evidence for mental state concepts corresponding to ‘want’ and
‘know’ even in chimpanzees, and the consensus that social attribution and mirror
self recognition are absent in other non-human primates and large-brained higher
vertebrates (Povinelli, 1989; 1993; Povinelli and Preuss 1995). There is
little room for argument about whether support for the mentalistic theories
requires behavioural evidence to distinguish mentalistic capacities from
alternative: — we should surely presume that natural selection is not
intelligent enough to be anything but behaviourist. Therefore if mentalistic
capacities are the result of selection they could only have arisen if they
produce behavioural effects which increase the inclusive fitness of the
individuals that possess them. The only reservation I have about the study of
perspective-taking proposed by Heyes is that the distinction between red-rimmed
and blue-rimmed goggles seems rather remote from any naturalistic function that
precursors to perspective-taking in wild chimpanzees might serve. One-way and
two-way silvered screens are suggested as alternatives and these would seem
better as a starting point, as more similar to completely opaque or partly
opaque vegetation. However, in any such stringent test, it seems quite
probable, on the basis of reports published so far, that chimpanzees would fail
the test.

In that case, should all discussion and experimentation on mentalistic cognitive
processes in non-human primates cease? It is unlikely that they would, since
although the experimental manipulations suggested by Heyes are helpful, there
are implicit and sometimes explicit theoretical assumptions related to the
‘theory of mind’ tests which are wider than any particular crucial experiment.
One underlying assumption is that non-human primates have enlarged brains by
general mammalian standards, and that the expansion of primate neocortex is to
some degree related to sociality (Humphrey, 1976). Data to test these
assumptions are still fairly limited (Barton, 1996), but presumably the large
brain size of primates is not an accident, and a function relation with
sociality could hold even if primate mentalistic capacities were very severely
limited by comparison with those demonstrated by the passing of false-belief
tests by human 10-year olds. Phylogenetic relatedness itself means that there
is special value in examination of the brain mechanisms of cognition in
primates, and the details of brain functioning, rather than the behavioural
effects of brain functioning, is an independent route to follow for evidence for
similarity between human and nonhuman mechanisms, even where human capacities
may be qualitatively different from those of any other extant species. There is
continuing interest in human and primate brain mechanisms for self-related
aspects of visual attention, and visually controlled reaching and
grasping(Graziano et al. 1994; Hietanen and Perrett 1996; Johnson et al. 1996;
Jeannerod et al. 1995; Kertzman et al. 1997; Witte et al. 1996). There is
already substantial evidence for a commonality in human and nonhuman primate
brain mechanism in at least some precursors to theory of mind tests.

In particular the integration and transformation of visual information into
representation of motor activity would be a prerequisite for imitation under
most definitions. Cells in macaque temporal cortex recognize direction of
motion and view of the body, and a proportion of these continue to be selective
when the information is limited to the movement of light patches attached to the
points of limb articulation (Oram and Perrett, 1994). Even more closely
related to precursors for imitation of object manipulation, there are cells in
parietal cortex which response to objects according type of manipulation (Murata
et al. 1996). These provide input to cells in premotor cortex of macaques,
which discharge either when the animal performs a grasping action itself (even
in the dark) or when it observes the human experimenter, or another monkey
perform the action (Rizzolatti et al. 1996). It has not unreasonably been
proposed that these cells may be part of an observation/execution matching
system (Gallese et al. 1996) which shows some degree of comparability between
macaques and humans (Fadiga et al. 1995; Grafton et al. 1996).

This does not imply at all that macaque capabilities for the purposive imitation
of grasping and gripping actions remotely equal those of humans and in a sense
this sort of special purpose sensory-motor transformation system is the
alternative to sweeping mentalistic accounts. There is also no reason to
suppose that some degree of multi-modal transformation of information does not
occur in the brains of rats (Chuder et al. 1995) and indeed even in the superior
colliculus of lower vertebrates (Spreckelsen et al. 1995). But in terms of
research strategies I would argue that a promising avenue of progress in primate
research related to theory of mind theories in humans would be investigation of
commonalities of brain mechanism. If functional brain imaging studies of
children, chimpanzees and macaques exposed to mirror self recognition
circumstances becomes feasible, and the pattern of activity observed in
ostensibly self-recognizing children and chimpanzees were found to be similar,
but something quite different was correlated with face touching in macaques, I
would regard this as evidence complementary to that obtained by purely
behavioural controls.

Vonhofsten, C, Siddiqui, A (1993) Using the mothers actions as a reference for
object exploration in 6-month-old and 12-month-old infants. British Journal
of Developmental Psychology, .11, .Pt1, .61-74.